Ibrahim

Today, I went into the staging building to see if there were any visible or otherwise apparent reasons for our L, P, Y M1 Transfer Function incoherence.

Here's what I did:

• Backed off all EQ stops, none were too close to touching, but the temp drif sag was higher yesterday than today so I just made sure they were all the way back.
• Re-did the foil, double triple checking nothing was touching, rubbing or in contact
• Checked every BOSEM Flag

Here's what I found:

• M1 is visibly pitched - this is corroborated by the 8-day drift of the F1 OSEM counts (as opposed to the daily sag and rebound of the LF-RT OSEMs. I've copied over the F1 section of the drift screenshot from yesterday's alog 79042 on this topic, since it seems the pitch instability suggestion from that alog was the right hypotehesis (F1 is used in P and is above the M1 center of mass). Image 1 shoes this clearly.
  • This could either be differential sagging of the Top Stage blades causing it to pitch in one direction over another.
  • It could also be a pitch hysteresis issue we had with the Top Mass during assembly - this was fixed by setting the heights of the blades to a different nominal position.
  • It could also be that the the Top Mass blades are differentially sagging too, causing more pull on one side than the other.
  • Or a combo, or something else.
• The M1 flags are surprisingly not visibly sagging that much - I guess this makes sense since 25 microns (our measured offset from centered position last week) is only 0.025mm.
• The M2 flags are much more visibly sagging, which means that the Top Mass blades are more affected by the temperature drift. This sort of corroborates the idea that the Top Mass blade sag is affecting the pitch moreso than the top stage blades or a previous ptich hysteresis blade height problem. Image 2 shoes one of the 4 M2 BOSEMs substantially lower than their centered positon.

Here's what I'm going to to:

I'm going to set an offset in order to "fake" center the BOSEMs and then take data but I expect that with a Pitch instability the results won't be too coherent either. We'll see. We're at least now ensured that there won't be any rubbing or contact.

What I'm going to do later:

We will fix the percieveable Roll issue on Monday when there are more hands on deck. I'll also consider re-centering the OSEMs at noon and measuring the temp at that time so we have some sort of informed reference.